914 H. H. NEWMAN AND J. THOMAS PATTERSON 
it appears that hereditary controlis almost perfect, as, for example, 
in set 4, where there is a difference of only one scute among the 
four foetuses; in other sets, 97 for example, the variation among 
the foetuses is so great that, were they not found to be enclosed 
in a common chorion, one would hardly believe them to be related. 
The same conditions prevail in connection with the atypical scutes 
or bands. In some sets the ‘abnormality’ is repeated in the dif- 
ferent individuals with the utmost fidelity of detail, while in others 
neither the extent of the region affected nor its location is at all 
rigidly defined. In a word, one can speak definitely as to the 
limits of hereditary control for only one set at a time. What 
appears to be true for one case does not apply exactly to another. 
Even here, then, where one would expect the phenomena of vari- 
ation and heredity to exhibit almost diagrammatic simplicity, 
we find a high degree of complexity and lack of uniformity; and 
one is again compelled to acknowledge that nature is baffling 
in her manifoldness of expression and in her freedom from the 
trammels of exact laws. 
SUMMARY 
1. The data derived from human identical twins cannot serve 
as a criterion for the determination of the limits of hereditary 
control, for two reasons: (a) ‘The origin of the two individuals 
from a single fertilized egg is assumed from the fact of resemblance. 
(b) The comparison between the twins is made only after years 
of post-natal life. 
2. Armadillo quadruplets furnish a reliable substitute for 
human identical twins, because: (a) The phenomenon of specific 
polyembryony has been demonstrated for the species. (b) The 
unborn foetuses, with all placental connections intact, are used. 
(c) The scutes of the nine bands of armor, which are the objects 
of the present investigation, are elements that reach their defini- 
tive number and arrangement long before birth, and hence are 
excellent for the study of heredity. 
3. A study of the morphology of the integument reveals the 
fact that the integumentary unit is a complex element made up 
of a bony plate, a horny scute and a well defined hair group. 
